Fuel vapor recirculation tubes are used in motor vehicle fuel tank filler tubes to recirculate fuel vapor during refueling from a nozzle inserted in the filler tube with a mechanical seal provided about the nozzle. The recirculated vapor provides a make-up flow below the nozzle seal to prevent the flow discharging from the nozzle from creating a vacuum in the filler tube and prematurely activating the automatic nozzle shutoff.
If the filler nozzle is working properly, the automatic nozzle shutoff mechanism will operate when the fuel tank is full. However, if the mechanism is not working properly, fuel is allowed to back up the filler tube and spill out to prompt the operator to manually shut off the nozzle.
Fuel systems typically have a “failed nozzle relief” (FNR) mechanism to protect the system from damage when it is overfilled. If the system includes a sealing member that seals against the filler nozzle to reduce vapor generation during refueling, the FNR mechanism provides an alternative flow path if the nozzle fails to shut off. This flow path is normally protected by a valve or a sealing membrane. However, the FNR mechanism needs to be reset and repositioned to a normal operating state after the failed nozzle event to close off the alternative flow path for the next normal refueling event. Resetting devices increase the complexity of the FNR mechanism and may also cause increased fuel tank pressures or fuel discharge at higher than accepted pressures.
There is a desire for a resettable FNR mechanism having a simple design and that can be easily reset by the operator.